Shell type centrifuge rotors are generally formed as a thin wall structure comprising in effect, a hollow shell. Rotors of this kind are well-known in the centrifuge art, having been in use since the earliest centrifuges. Modern high-speed centrifuges operate in force regimes that require high-strength rotors machined from solid forgings. Current use of shell type rotors, therefore, is limited to moderate speed analytical centrifuges. Typically, centrifuges of this type are of table top size and designed to be very inexpensive compared to high performance analytical centrifuges.
In designing a centrifuge, safety is a paramount concern. In the case of the moderate speed centrifuge which is typically designed for sale in a highly competitive market, this concern for safety is closely followed by concern for economy of manufacture. Ideally, the design of the centrifuge rotor should aim not only at minimizing the fabrication cost of the rotor, but it should also contribute to every possible economy in the design of other elements of the centrifuge. One way of achieving this aim, is to simply reduce the mass of the rotor as much as practicable. In so doing, the structure of the rotor chamber can be made somewhat less rugged. In the event of a mishap to the rotor, the amount of kinetic energy that the chamber will have to safely absorb will be lower, and thus, the overall size and cost of the centrifuge can be reduced.
Another advantage to reducing the mass of the rotor is that it reduces its inertia, enabling it to be driven with less power. A smaller, less expensive motor can therefore be used. The amount of required motor power can be yet further reduced by designing the rotor so as to have low windage (i.e. aerodynamic drag).
Among other considerations relating to the design of rotors for centrifuges of the class under discussion, is a problem associated with tube breakage. This problem arises with the use of both plastic and glass sample tubes which occasionaly break under the stress of centrifugation forces. In such event, some means must be provided to prevent spillage of the tube contents into the rotor chamber. Small centrifuges typically are not equipped with seals in the rotor chamber to prevent damage to the drive system from fluids. On the contrary, many small centrifuges incorporate openings in the rotor chamber in order to utilize the air stream produced by the rotor's fan effect as a means of cooling the motor. Some designers have dealt with the problem by employing a tube adapter in which to house each sample tube. Such adapters are typically molded of plastic in a form somewhat resembling a test tube. Each adapter is designed to receive and support a sample tube, comprising in effect, a closed bottom cavity for the sample tube. While the use of such adapters adequately deals with the problem of retaining samples in the event of tube breakage, the use of adapters is generally disadvantageous because they contribute to the overall mass of the rotor and represent an additional element of cost.
Accordingly, the foregoing discussion has identified a number of problems associated with the manufacture of low-cost, moderate speed centrifuges and proposed certain design remedies therefor. The successful integration of these and certain other design features into a practical rotor is the subject of the present invention.